Hand held drilling and/or hammering tools are know which can be used with a dust collection unit accessory. The collection unit, may be releaseably mechanically mounted on the tool and will generally comprise a shroud for collecting dust from the region of a tool or bit of the tool, a dust collection chamber, a filter and a system for generating an airflow into and through the shroud, the chamber and the filter. Dust and debris generated by the tool or bit of the tool will be entrained in this airflow and so will be pulled into the shroud and into the chamber. As the air passes through the filter, any dust or debris entrained within it will be deposited in the chamber.
The system for generating the airflow will generally include a fan, which fan may be housed in the tool or in the dust collection unit. When the fan is housed in the tool, it is powered by the motor of the tool and it may have the dual function of also generating an airflow which cools components of the tool. An outlet from the dust collection unit will mate with an inlet to the fan of the tool in order to generate the airflow in the dust collection unit. When the fan is housed in the dust collection unit, it is known to power the fan by using the motor of the tool, for example by an end of the tool motor armature shaft engaging a shaft of the fan to rotatingly drive the fan. A problem with these types of dust collection units is that the fan is driven at the speed of rotation of the motor of the tool and so an optimum motor speed for the tool and not for the fan is selected for the speed of rotation of the motor. In addition the speed of rotation of the motor may reduce, for example, when the tool is working hard. Therefore, the speed of the motor is not selected to be the optimum speed for the fan.
A separate motor can be used for powering the fan of the dust collection unit, which motor is mounted within a housing of the dust collection unit. This has the advantage that the characteristics of the motor can be specifically tailored to optimise the airflow through the dust collection unit. However, some means is required for connecting the motor of the dust collection unit to a power supply.